Keywords: Li-ion batteries, intercalation cathodes, disordered rock salt, Li 2 VO 2 F Advanced cathode materials with superior energy storage capability are highly demanded for mobile and stationary applications. The inherent structural feature of Li + hosts is critical for the battery performance. High-capacity conversion cathode materials often encounter large voltage hysteresis (low energy efficiency) accompanied with the structural reconstruction.[1]The current commercial cathode materials are still dominated by intercalation materials with intrinsic structural integrity for accommodating Li + .[2] However, the known intercalation materials have limited theoretical capacity (< 300 mAh g -1 ). [3] In addition, structural transition/degradation have often been observed for the common intercalation hosts with ordered Li + / transition metal (TM) lattice sites. Antisite disorder (Li + sites/layers occupied by TM ions) in olivines can block the one-dimensional Li + diffusion path.[4] The activation barrier for Li + diffusion in layered oxides is sensitive to the Li-content, the spacing of the

The utilization of intermittent renewable energy sources needs low-cost, reliable energy storage systems in the future. Among various electrochemical energy storage systems, redox flow batteries (RFBs) are promising with merits of independent energy storage and power generation capability, localization flexibility, high efficiency, low scaling-up cost, and excellent long charge/discharge cycle life. RFBs typically use metal ions as reacting species. The most exploited types are all-vanadium RFBs (VRFBs). Here, we discuss the core components for the VRFBs, including the development and application of different types of membranes, electrode materials, and stack system. In addition, we introduce the recent progress in the discovery of novel electrolytes, such as redox-active organic compounds, polymers, and organic/inorganic suspensions. Versatile structures, tunable properties, and abundant resources of organic-based electrolytes make them suitable for cost-effective stationary applications. With the active species in solid form, suspension electrolytes are expected to provide enhanced volumetric energy densities.

Mixed-anion materials for Li-ion batteries have been attracting attention in view of their tunable electrochemical properties. Herein, we compare two isostructural (Fm3̅m) model intercalation materials Li2VO3 and Li2VO2F with O(2-) and mixed O(2-)/F(-) anions, respectively. Synchrotron X-ray diffraction and pair distribution function data confirm large structural similarity over long-range and at the atomic scale for these materials. However, they show distinct electrochemical properties and kinetic behaviour arising from the different anion environments and the consequent difference in cationic electrostatic repulsion. In comparison with Li2VO3 with an active V(4+/5+) redox reaction, the material Li2VO2F with oxofluoro anions and the partial activity of V(3+/5+) redox reaction favor higher theoretical capacity (460 mA h g(-1)vs. 230 mA h g(-1)), higher voltage (2.5 V vs. 2.2 V), lower polarization (0.1 V vs. 0.3 V) and faster Li(+) chemical diffusion (∼10(-9) cm(2) s(-1)vs. ∼10(-11) cm(2) s(-1)). This work not only provides insights into the understanding of anion chemistry, but also suggests the rational design of new mixed-anion battery materials.

New high‐capacity intercalation cathodes of Li2VxCr1−xO2F with a stable disordered rock salt host framework allow a high operating voltage up to 3.5 V, good rate performance (960 Wh kg−1 at ≈1 C), and cycling stability.

In this work, LiMnTiO4 (a structural analogue of classic spinel LiMn2O4) with a disordered cubic spinel structure (Fd3̅m) has been synthesized by a low-temperature sol–gel route. The as-obtained LiMnTiO4 exhibits excellent cycling stability in a wide voltage range from 1.5 to 4.8 V with high discharge capacities of 290, 250, and 140 mA h g–1 at a C/40, C/19, and 1C rate, respectively. Combined long- and short-range structural characterization techniques are used to reveal the correlation between structure and electrochemical behavior. During cycling, the charge/discharge profiles of LiMnTiO4 evolve from initially two well-separated plateaus into sloping regimes. In the early stage of discharge, LiMnTiO4 undergoes phase transitions from an initial spinel phase to mixtures of predominant rock-salt (Fm3̅m) and tetragonal (I41/amd) structures along with a decrease in crystallite size from 12 nm to 3 to 4 nm. During further cycling, the spinel/rock-salt phase transition was found to be reversible with the cubic framework remaining intact. The presence of the tetragonal phase after the first discharge suggests that the Mn3+ Jahn–Teller distortion is partially involved during lithiation from Li1–y Mn3+y TiO4 to Li1+x Mn3–x TiO4 and the fraction of such a tetragonal phase remains at about 30–40% during subsequent cycling.

Sol-gel Ru(0.3)Sn(0.7)O(2) electrode coatings with crack-free and mud-crack surface morphology deposited onto a Ti-substrate are prepared for a comparative investigation of the microstructural effect on the electrochemical activity for Cl(2) production and the Cl(2) bubble evolution behaviour. For comparison, a state-of-the-art mud-crack commercial Ru(0.3)Ti(0.7)O(2) coating is used. The compact coating is potentially durable over a long term compared to the mud-crack coating due to the reduced penetration of the electrolyte. Ti L-edge X-ray absorption spectroscopy confirms that a TiO(x) interlayer is formed between the mud-crack Ru(0.3)Sn(0.7)O(2) coating and the underlying Ti-substrate due to the attack of the electrolyte. Meanwhile, the compact coating shows enhanced activity in comparison to the commercial coating, benefiting from the nanoparticle-nanoporosity architecture. The dependence of the overall electrode polarization behaviour on the local activity and the bubble evolution behaviour for the Ru(0.3)Sn(0.7)O(2) coatings with different surface microstructure are evaluated by means of scanning electrochemical microscopy and microscopic bubble imaging.

Nanocrystalline Li2Fe1‑y Mn y SiO4 (y = 0, 0.2, 0.5, 1) powders with in situ carbon coating have been prepared by a sol–gel route and their structural evolution during the first electrochemical charge–discharge cycles has been investigated in detail by X-ray diffraction in combination with 7Li MAS NMR, 57Fe Mössbauer spectroscopy and in situ X-ray absorption spectroscopy. These results provide detailed information about the amorphization, phase transitions and the partially reversible change in the local environment of Li nuclei upon cycling. The redox processes of the metal cations responsible for the cycling performance of the first few cycles and for the cyclability are also derived from the combined structural characterizations.

Li-ion batteries have driven the technological evolution of portable electronics, automotive, and stationarya pplications over the past decades.[1] However, the poor low-temperature performance of Li-ion batteries impedes their specific applications, such as fora erospace, defense, and transportation systems.[2] When operating at reduced temperatures, especially below 0 8C, the kinetic performance of the employed materials, governed by the intrinsic transport property for electrons and Li ions, becomes ac ritical factor determining the deliverable capacity.[3] Classic Li-ion battery cathode materials suffer from substantial capacity loss, [4] severe voltage hysteresis, [5] and change in voltage profiles.[6] As reported, from 25 to 0 8C, ac ommercialL iFePO 4 -based cell has ac apacity retention of only 42 %. [7] The sluggish kinetics of Li + transport and the reduced electronic conductivity in the solid LiFePO 4 phase at low temperatures leads to the voltage profiles evolving from ap lateau-like to sloping regime.[8] For layered Ni-Mn-Co oxides, [9] ad ischarge voltage downshift of 0.5 Vh as been observed when reducing the temperature from 25 to À20 8C. [6] In addition, the performance deteriorationo fa node materials and the appliede lectrolytes at low temperatures contributet ot he poor overall battery performance. [2,10] At sub-ambient temperatures, Li platingt ends to occur at the graphite anode,o wing to the reduced Li + intercalation into graphite.[11] At temperatures below À10 8C, the ionic mobility in the electrolyte solution and conductivity of the conventional binary carbonate electrolyte fall rapidly.[12] The optimization of the electrolyte formulations for different electrode materials at low temperatures still remains to be solved. Nevertheless, exploring new cathodem aterials with well-retaineds pecific energiesa tr educed temperatures is am ore decisive step towards broad applications of Li-ion batteries.We have recentlyr eportedt hat an ew cathode material, Li 2 VO 2 F, with ad isordered rock-salt structure can deliver ah igh initial intercalation capacity when cycling at al ow current rate.[13] However,L i 2 VO 2 Fs uffers from capacity fading whilst cycling. It has been found that the poor cycling performance of Li 2 VO 2 Fc an be improved by substituting Cr forVi nt his system.[14] Moreover,t he cyclability of the mixed V/Cr oxyfluorides depends on the applied chargecutoff voltages and operation temperature. Af acile Li + chemical diffusion in such ac lass of materials favors the kinetic properties.[15] Herein,w ee xplore the composition-dependent, low-temperature properties of the oxyfluorides and examine the structural features responsible for the cycling performance.The low-temperature rate capabilities of Li 2 VO 2 F, Li 2 CrO 2 F, and Li 2 Cr 0.2 V 0.8 O 2 Fw ere first evaluated at À10 8Ca tv arious current densities from 26 to 1050 mA g À1 ,a nd then back again at 26 mA g À1 (Figures 1a-c